1. Field
The present invention relates generally to electric power storage and generation. More particularly, the present invention provides a system for potential energy storage employing electrically driven rail consists (a consist is defined herein as multiple train car elements) carrying off loadable masses between lower and upper storage facilities for potential energy storage by employing electrical grid power to the consists for transport of the masses from the lower to upper storage facility and potential energy recovery and return to the electrical grid by electromagnetic regenerative braking of the consists during transport of the masses from the upper to lower storage facility with ancillary support including variable and reactive power support and regulation up and down trimming capability.
2. Related Art
The electric power grid is increasingly complex and the matching of power generation supply with power usage is a critical element in maintaining stability in operation. This issue is becoming more complicated with the addition of alternative energy generation sources such as wind power and solar power which have inherent issues with consistency of power production. The need for utility scale energy storage as a portion of the power supply grid is driven by increasing requirements for daily load shifting and power quality services including frequency regulation, voltage control, spinning reserve, non-spinning reserve and black start. It is presently estimated that energy storage power requirements in the US will approach 200,000 MW for load shifting and exceed 20,000 MW for power quality service.
Electrical energy storage may be accomplished using battery technologies, capacitor storage systems, kinetic energy storage systems such as flywheels or potential energy storage systems. Battery technology for Lithium ion batteries, flow batteries and Rechargeable Sodium-Sulfur batteries (NaS) are improving but typically will provide estimated capability only in the range of 50 MW or less. Similarly, capacitive storage systems on reasonable scale only provide between 1-10 MW of capability. Flywheel storage systems are also typically limited to less than 20 MW due to physical size and structural materials constraints.
Conventional potential energy storage devices consist of mechanical lifting devices raising weights against the force of gravity and Pumped Hydro, a method that stores energy in the form of water pumped uphill against the force of gravity. Mechanical lifting devices are limited in their height to a few hundred feet and therefore require large amounts of mass to store a significant amount of electric energy. This results in a very large cost, making these devices expensive and uneconomical. In Pumped Hydro, water is pumped from a lower elevation reservoir to a higher elevation; the stored water is then released through turbines to convert the stored energy into electricity upon demand. The round-trip storage cycle efficiency losses of such systems are typically in the range of 25% and the difficulties in permitting, constructing and operating makes pumped hydro difficult to implement. It can take more than a decade to construct such a system.
It is therefore desirable to provide potential energy storage with capability in the power generation range of 100-2,000 MW with high efficiency and reduced installation and capital investment requirements.